Lunar and solar cycles recorded in the skeleton of a Jurassic solitary coral

Abstract

Regular growth increments have been identified in the epitheca of the Bathonian solitary coral Montlivaltia Lamouroux, 1821. Examination of a large population of specimens from several outcrops across Lorraine (France) shows that these cyclic patterns are recurrent and can be consistently recognized. The dimensional ratios between successive increments suggest that the observed periodicities reflect lunar cycles nested within annual growth rhythms. This interpretation allows for the estimation of coral age and provides a means to document how morphological parameters vary through ontogeny. It therefore offers a valuable alternative to the debated practice of using size as a proxy for age in evolutionary studies. Finally, the regularity of the growth cycles further supports the view that Montlivaltia was solitary but probably harbored zooxanthellae.